On the P-coordinating limit of NHC-phosphenium cations toward Rh(I) centers

Two types of imidazoliophosphane with additional electron-withdrawing substituents, such as alkoxy or imidazolio groups, are experimentally described and theoretically studied. Diethyl N,N'-2,4,6-methyl(phenyl)imidazoliophosphonite is shown to retain a P-coordinating ability toward a {RhCl(cod)} (cod = cycloocta-1,5-diene) center, thus competing with the cleavage of the labile C-P bond. Derivatives of N,N'-phenylene-bridged diimidazolylphenylphosphane were isolated in good yield. Whereas the dicationic phosphane proved to be inert in the presence of [{RhCl(cod)}(2)], the monocationic counterpart was shown to retain the P-coordinating ability toward a {RhCl(cod)} center, thus competing with the N-coordinating ability of the nonmethylated imidazolyl substituent. The ethyl phosphinite version of the dication, thus possessing an extremely electron-poor P(III) center, was also characterized. According to the difference between the calculated homolytic and heterolytic dissociation energies, the N(2)C???P bond of imidazoliophosphanes with aryl, amino, or alkoxy substituents on the P atom is shown to be of dative nature. The P-coordinating properties of imidazoliophosphanes with various combinations of phenyl or ethoxy substituents on the P atom and those of six diimidazolophosphane derivatives with zero, one, or two methylium substituents on the N atom, were analyzed by comparison of the corresponding HOMOs and LUMOs and by calculation of the IR C=O stretching frequencies of their [RhCl(CO)(2)] complexes. Comparison of the ν(CO) values allows the family of the electron-poor Im(+) PRR' (Im = imidazolyl) potential ligands to be ranked in the following order versus (R,R'): P(OEt)(3)<(Ph,Ph)<(Ph,OEt)<(OEt,OEt)相似文献   

Reactivity of TpMe2‐Supported Yttrium Alkyl Complexes toward Aromatic N‐Heterocycles: Ring‐Opening or CC Bond Formation Directed by CH Activation

Unusual chemical transformations such as three‐component combination and ring‐opening of N‐heterocycles or formation of a carbon–carbon double bond through multiple C–H activation were observed in the reactions of Tp^Me2‐supported yttrium alkyl complexes with aromatic N‐heterocycles. The scorpionate‐anchored yttrium dialkyl complex [Tp^Me2Y(CH₂Ph)₂(THF)] reacted with 1‐methylimidazole in 1:2 molar ratio to give a rare hexanuclear 24‐membered rare‐earth metallomacrocyclic compound [Tp^Me2Y(μ‐N,C‐Im)(η²‐N,C‐Im)]₆ ( 1 ; Im=1‐methylimidazolyl) through two kinds of C–H activations at the C2‐ and C5‐positions of the imidazole ring. However, [Tp^Me2Y(CH₂Ph)₂(THF)] reacted with two equivalents of 1‐methylbenzimidazole to afford a C–C coupling/ring‐opening/C–C coupling product [Tp^Me2Y{η³‐(N,N,N)‐N(CH₃)C₆H₄NHCH?C(Ph)CN(CH₃)C₆H₄NH}] ( 2 ). Further investigations indicated that [Tp^Me2Y(CH₂Ph)₂(THF)] reacted with benzothiazole in 1:1 or 1:2 molar ratio to produce a C–C coupling/ring‐opening product {(Tp^Me2)Y[μ‐η²:η¹‐SC₆H₄N(CH?CHPh)](THF)}₂ ( 3 ). Moreover, the mixed Tp^Me2/Cp yttrium monoalkyl complex [(Tp^Me2)CpYCH₂Ph(THF)] reacted with two equivalents of 1‐methylimidazole in THF at room temperature to afford a trinuclear yttrium complex [Tp^Me2CpY(μ‐N,C‐Im)]₃ ( 5 ), whereas when the above reaction was carried out at 55 °C for two days, two structurally characterized metal complexes [Tp^Me2Y(Im‐Tp^Me2)] ( 7 ; Im‐Tp^Me2=1‐methyl‐imidazolyl‐Tp^Me2) and [Cp₃Y(HIm)] ( 8 ; HIm=1‐methylimidazole) were obtained in 26 and 17 % isolated yields, respectively, accompanied by some unidentified materials. The formation of 7 reveals an uncommon example of construction of a C?C bond through multiple C–H activations.     

Vielseitige Koordinationschemie von Vanadium(V): Substitutionsreaktionen,Umlagerungen und Kondensationsreaktionen von Oxovanadium(V)‐Komplexen des tripodalen Sauerstoffliganden LOMe− = [η5‐(C5H5)Co{P(OMe)2(O)}3]−

Multifaceted Coordination Chemistry of Vanadium(V): Substitution, Rearrangement Reactions, and Condensation Reactions of Oxovanadium(V) Complexes of the Tripodal Oxygen Ligand L_OMe^? = [η⁵‐(C₅H₅)Co{P(OMe)₂(O)}₃]^? The octahedral oxovanadium(V) complex [V(O)F₂L_OMe] of the tripodal oxygen ligand L_OMe^? = [η⁵‐(C₅H₅)Co{P(OMe)₂(O)}₃]^? reacts with alcohols and phenol with substitution of one fluoride ligand to form alkoxo complexes [V(O)F(OR)L_OMe], R = Me, Et, i‐Prop, Ph. In the presence of water, however, both fluoride ions are substituted and a complex with the composition VO₂L_OMe can be isolated. The crystal structure shows that the oxo‐bridged trimer [{V(O)(L_OMe)O}₃] was synthesized. In the presence of BF₃ the fluoride ligand in the alkoxo‐complex [V(O)F(OEt)L_OMe] can be exchanged for pyridine to yield [V(O)(OEt)pyL_OMe]BF₄. Analogous attempts to exchange the fluoride ligand for tetrahydrofuran and acetonitrile induces a rearrangement reaction that leads to the vanadium complex [V(O)(L_OMe)₂]BF₄. The crystal structure of this compound has been determined. Its ¹H and ³¹P‐NMR spectra show that it is a highly fluxional vanadium complex at ambient temperature in solution. The two tripodal ligands L_OMe^? coordinate the vanadium centre as bidentate or tridentate ligands. The exchange bidentate/tridentate becomes slow on the NMR time scale below about 200 K.     

Aggregation of Dinuclear Cations [{Au(PR3)}2(μ‐OH)]+ into Dimers Induced by Polyoxometalate (POM) Template Effects

Intercluster compounds, [{(Au{P(p‐XPh)₃})₂(μ‐OH)}₂][α‐SiMo₁₂O₄₀(Au{P(p‐XPh)₃})₂] · nEtOH [X = F ( 1 ), Cl ( 2 )] were synthesized by polyoxometalate (POM)‐mediated clusterization, and were unequivocally characterized by X‐ray crystallography, elemental analysis, thermogravimetric and differential thermal analysis (TG/DTA), Fourier transform infrared (FT‐IR), solid‐state cross‐polarization magic‐angle‐spinning (CPMAS) ³¹P nuclear magnetic resonance (NMR), and solution (¹H, ³¹P{¹H}) NMR spectroscopy. The “dimer‐of‐dinuclear phosphanegold(I) cation”, i.e., [{(Au{P(p‐XPh)₃})₂(μ‐OH)}₂]²⁺ was formed by the self‐assembly of dinuclear phosphanegold(I) cations, i.e., [(Au{P(p‐XPh)₃})₂(μ‐OH)]⁺, through inter‐cationic aurophilic interactions as the crossed‐edge arrangement (or tetrahedral Au₄ structure) for 1 , while as the parallel‐edge arrangement (or rectangular Au₄ structure) for 2 . The latter arrangement was first attained only by assistance of the POM. The POM anions in 1 and 2 contained two mononuclear phosphanegold(I) cations, i.e., [Au{P(p‐XPh)₃}]⁺, linked to the OMo₂ oxygen atoms of edge‐sharing MoO₆ octahedra. In the solution ³¹P{¹H} NMR of 1 and 2 , we observed single signals due to the rapid exchange of the phosphanegold(I) units. This shows that the OMo₂ oxygen atoms of edge‐sharing MoO₆ octahedra in the Keggin POM act as multi‐centered active binding sites for the formation of [{(Au{P(p‐XPh)₃})₂(μ‐OH)}₂]²⁺.     

Formation,Dynamic Behavior,and Chemical Transformation of Pt Complexes with a Rotaxane‐like Structure

The reaction of [Pt(CH₂COMe)(Ph)(cod)] (cod=1,5‐cyclooctadiene) with (ArCH₂NH₂CH₂‐C₆H₄COOH)⁺(PF₆)^? (Ar=4‐tBuC₆H₄ or 9‐anthryl) in the presence of cyclic oligoethers such as dibenzo[24]crown‐8 (DB24C8) and dicyclohexano[24]crown‐8 (DC24C8) produces {(ce)[ArCH₂NH₂CH₂C₆H₄COOPt(Ph)(cod)]}⁺(PF₆)^? (ce=DB24C8 or DC24C8, Ar=4‐tBuC₆H₄ or 9‐anthryl) with interlocked structures. FABMS and NMR spectra of a solution of these compounds indicate that the Pt complexes with a secondary ammonium group and DB24C8 (or DC24C8) make up the axis and cyclic components, respectively. Temperature‐dependent ¹H NMR spectra of a solution of {(DB24C8)[4‐tBuC₆H₄CH₂NH₂CH₂‐C₆H₄COOPt(Ph)(cod)]}⁺(PF₆)^? ({(DB24C8)[ 4 ‐H]}⁺(PF₆)^?) show equilibration with free DB24C8 and the axis component. The addition of DB24C8 to a solution of {(DC24C8)[ 4 ‐H]}⁺(PF₆)^? causes partial exchange of the macrocyclic component of the interlocked molecules, giving a mixture of {(DC24C8)[ 4 ‐H]}⁺(PF₆)^?, {(DB24C8)[ 4 ‐H]}⁺(PF₆)^?, and free macrocyclic compounds. The reaction of 3,5‐Me₂C₆H₃COCl with {(DB24C8)[ 4 ‐H]}⁺(PF₆)^? affords the organic rotaxane {(DB24C8)(4‐tBuC₆H₄CH₂NH₂CH₂‐C₆H₄COOCOC₆H₃Me₂‐3,5)}⁺(PF₆)^? through C? O bond formation between the aroyl group and the carboxylate ligand of the axis component. The addition of 2,2′‐bipyridine (bpy) to a solution of {(DB24C8)[ 4 ‐H]}⁺(PF₆)^? induces the degradation of the interlocked structure to form a complex with trigonal bipyramidal coordination, [Pt(Ph)(bpy)(cod)]⁺(PF₆)^?, whereas the reaction of bpy with [Pt(OCOC₆H₄Me‐4)(Ph)(cod)] produces the square‐planar complex [Pt(OCOC₆H₄Me‐4)(Ph)(bpy)].     

1,2,4‐Triazol‐3‐ylidenes with an N‐2,4‐Dinitrophenyl Substituent as Strongly π‐Accepting N‐Heterocyclic Carbenes

The synthesis and characterisation of a series of new Rh and Au complexes bearing 1,2,4‐triazol‐3‐ylidenes with a N‐2,4‐dinitrophenyl (N‐DNP) substituent are described. IR, NMR, single‐crystal X‐ray diffraction and computational analyses of the Rh complexes revealed that the N‐heterocyclic carbenes (NHCs) behaved as strong π acceptors and weak σ donors. In particular, a natural bond orbital (NBO) analysis revealed that the contributions of the Rh→C_carbene π backbonding interaction energies (ΔE_bb) to the bond dissociation energies (BDE) of the Rh? C_carbene bond for [RhCl(NHC)(cod)] (cod=1,5‐cyclooctadiene) reached up to 63 %. The Au complex exhibited superior catalytic activity in the intermolecular hydroalkoxylation of cyclohexene with 2‐methoxyethanol. The NBO analysis suggested that the high catalytic activity of the Au^I complex resulted from the enhanced π acidity of the Au atom.     

NNP‐Type Pincer Imidazolylphosphine Ruthenium Complexes: Efficient Base‐Free Hydrogenation of Aromatic and Aliphatic Nitriles under Mild Conditions

A series of seven novel N^ImN^HP‐type pincer imidazolylphosphine ruthenium complexes has been synthesized and fully characterized. The use of hydrogenation of benzonitrile as a benchmark test identified [RuHCl(CO)(N^ImN^HP^tBu)] as the most active catalyst. With its stable Ru?BH₄ analogue, in which chloride is replaced by BH₄, a broad range of (hetero)aromatic and aliphatic nitriles, including industrially interesting adiponitrile, has been hydrogenated under mild and base‐free conditions.     

Facile Synthesis of Phosphaamidines and Phosphaamidinates using Nitrilium Ions as an Imine Synthon

Readily accessible nitrilium triflates are convenient imine building blocks for the expedient synthesis of a novel class of 1,3‐P,N ligands as demonstrated for the reaction with primary phosphanes. This procedure allows variation of all substituents. X‐ray crystal structures are reported for nitrilium ions, phosphaamidines, and three phosphaamidinate complexes. The lithium phosphaamidinate is N coordinated and its reaction with [AuCl(tht)] (tht=tetrahydrothiophene) gives a unique P‐bridged gold trimer, while a P,N‐bidentate complex results from [{RhCl(cod)}₂]. The nitrilium ion methodology allows extension of the 1,3‐P,N motive to bis(imino)phosphanes, which are the neutral phosphorus analogues of the valuable β‐diketiminate ligand.     

Copper(I) Complexes of Anionic Tridentate CNC Pincer Ligands

New monoanionic CNC pincer ligands, [N{SiMe₂CH₂(RIm)}₂]^– (R = tBu, iPr, Ph) featuring three different N-heterocyclic carbenes and a disilylamido moiety is reported. Treatment of the lithium salt of [N{SiMe₂CH₂(RIm)}₂]^– with Cu^IOTf afforded the corresponding copper complexes [N{SiMe₂CH₂(RIm)}₂]Cu in 41–56 % yield. X-ray crystal structures of [N{SiMe₂CH₂(RIm)}₂]Cu show that they are monomeric and feature three-coordinate, pseudo T-shaped copper(I) sites. The X-ray crystal structure of one of the precursor lithium complexes, [N{SiMe₂CH₂(tBuIm)}₂]Li is also presented.     

Single Oxygen‐Atom Insertion into PB Bonds: On‐ and Off‐Metal Transformation of a Borylphosphine into a Borylphosphinite

An oxygen atom is selectively inserted into the P?B bond of a borylphosphine ( L₁ ) by reaction with Me₃NO to afford the corresponding borylphosphinite ( L₂ ). This transformation can also be effected when L₁ is coordinated to rhodium. The ν(CO) values for trans‐[RhCl(CO)(L)₂] reveal very different electronic properties for coordinated L₁ and L₂ which translate into the strikingly different performances of the complexes [RhCl(L)(cod)] (L= L₁ or L₂ , cod=1,5‐cyclooctadiene) in hydrosilylation and hydroboration catalysis.     

Synthesis,Characterisation and In Vitro Anticancer Activity of Hexanuclear Thiolato‐Bridged Arene Ruthenium Metalla‐Prisms

Hexanuclear thiolato‐bridged arene ruthenium metalla‐prisms of the general formula [(p‐cymene)₆Ru₆(SR)₆(tpt)₂]⁶⁺ (R=CH₂Ph, CH₂C₆H₄‐p‐tBu, CH₂CH₂Ph; tpt=2,4,6‐tris(4‐pyridyl)‐1,3,5‐triazine), obtained from the dinuclear precursors [(p‐cymene)₂Ru₂(SR)₂Cl₂], AgCF₃SO₃ and tpt, have been isolated and fully characterised as triflate salts. The metalla‐prisms are highly cytotoxic against human ovarian cancer cells, especially towards the cisplatin‐resistant cell line A2780cisR (IC₅₀ <0.25 μM ).     

Nickelphosphankomplexe der Mercaptoessigsäure

Nickel Complexes of Mercaptoacetic Acid The reaction of [Cp°₂Zr(OOCCH₂SH‐κ¹O)(OOCCH₂SH‐κ²O, O′)] (Cp° = C₅EtMe₄) with [NiCl₂(PMe₂Ph)₂] or [NiCl₂(dppe)] (dppe = PPh₂CH₂CH₂PPh₂) in the presence of NEt₃ yields the tetranuclear Zr^IV/Ni^II complex [{Cp°₂Zr(κ¹O‐OOCCH₂S‐κ²O′, S)(κ²O, O′‐OOCCH₂S‐κ¹S)Ni(PMe₂Ph)}₂] ( 1 ) and the chelate complexes [Ni(OOCCH₂S‐κ²O, S)L₂] [L = PMe₂Ph ( 2 ), L₂ = dppe ( 3 )]. 2 and 3 are also accessible from [NiCl₂(PMe₂Ph)₂] or [NiCl₂(dppe)] and mercaptoacetic acid in the presence of NEt₃ in quantitative yield. The structure of 2 is dynamic in solution, whereby a complex with three‐coordinate nickel atom is formed. 2 and 3 were characterized spectroscopically (¹H, ¹³C, ³¹P NMR and IR) and by crystal structure determination.     

Phosphorus Ligands with a Large Cavity: Synthesis of Triethynylphosphines with Bulky End Caps and Application to the Rhodium‐Catalyzed Hydrosilylation of Ketones

Trialkynylphosphines substituted with bulky triarylsilyl groups at the alkyne termini were synthesized. The new phosphines P(C?CSiAr₃)₃ (Ar=3,5‐tBu₂‐4‐MeOC₆H₂, 3,5‐(Me₃Si)₂C₆H₃) are uncrowded near the phosphorus atom but bulky in the distal region. As a result, they contain a large cavity, at the bottom of which the phosphine lone‐pair electrons are located. The compounds are stable to oxidation by air and hydrolysis. DFT calculations suggested that the triethynylphosphines are good π‐acceptor ligands, comparable with P(OAr)₃. The trialkynylphosphines reacted with [{RhCl(cod)}₂] (P/Rh=1.1:1) to give selectively the monophosphine–rhodium complex [RhCl(cod)P(C?CSiAr₃)₃]. X‐ray crystal‐structure analysis revealed that the {RhCl(cod)} fragment is fully accommodated by the cavity of the phosphine ligand. Compared to the effect of analogues with smaller end caps and PPh₃, the trialkynylphosphines accelerated markedly the rhodium‐catalyzed hydrosilylation of ketones with a triorganosilane. It is proposed that the higher catalytic activity observed with the holey phosphines is a result of the preferential formation of a monophosphine–rhodium species.     

Synthese von Oxovanadium(V)‐halogeno‐Komplexen der tripodalen Sauerstoffliganden LR— = [η5‐(C5H5)Co{PR2(O)}3]—, R = OMe,OEt

Syntheses of Oxovanadium(V) Halide Complexes Stabilized with Tripodal Oxygen Ligands L_R^— = [η⁵‐(C₅H₅)Co{PR₂(O)}₃]^—, R = OMe, OEt The sodium salts of the tripodal oxygen ligands L_R^— = [η⁵‐(C₅H₅)Co{PR₂(O)}₃]^— (R = OMe, OEt) react with the oxovanadium halides V(O)F₃ and V(O)Cl₃ to yield deep red compounds of the type [V(O)X₂L_R]. Halide exchange reactions with [V(O)Cl₂L_OMe] und [V(O)F₂L_OMe] aiming at the preparation of the analogous bromide complex [V(O)Br₂L_OMe] led to the isomer [VO(L_OMe)₂][V(O)Br₄]. The crystal structure of [V(O)Cl₂L_OMe] has been determined by single crystal x‐ray diffraction. The compound crystallizes in the monoclinic space group P2₁/n with a = 9.6332(8), b = 15.0312(11) and c = 15.3742(12)Å, β = 100.181(8)°. The coordination around vanadium is distorted octahedral.     

A Facile Route to Backbone‐Tethered N‐Heterocyclic Carbene (NHC) Ligands via NHC to aNHC Rearrangement in NHC Silicon Halide Adducts

The reaction of 1,3‐diisopropylimidazolin‐2‐ylidene (iPr₂Im) with diphenyldichlorosilane (Ph₂SiCl₂) leads to the adduct (iPr₂Im)SiCl₂Ph₂ 1 . Prolonged heating of isolated 1 at 66 °C in THF affords the backbone‐tethered bis(imidazolium) salt [(^aHiPr₂Im)₂SiPh₂]²⁺ 2 Cl^? 2 (“^a” denotes “abnormal” coordination of the NHC), which can be synthesized in high yields in one step starting from two equivalents of iPr₂Im and Ph₂SiCl₂. Imidazolium salt 2 can be deprotonated in THF at room temperature using sodium hydride as a base and catalytic amounts of sodium tert‐butoxide to give the stable N‐heterocyclic dicarbene (^aiPr₂Im)₂SiPh₂ 3 , in which two NHCs are backbone‐tethered with a SiPh₂ group. This easy‐to‐synthesize dicarbene 3 can be used as a novel ligand type in transition metal chemistry for the preparation of dinuclear NHC complexes, as exemplified by the synthesis of the homodinuclear copper(I) complex [{^a(ClCu?iPr₂Im)}₂SiPh₂] 4 .     

Iridium Complexes of 2,2′‐Bidipyrrins

The reaction of [{Ir(cod)(μ‐Cl)}₂] and K₂CO₃ or of [{Ir(cod)(μ‐OMe)}₂] alone with the non‐natural tetrapyrrole 2,2′‐bidipyrrin (H₂BDP) yields, depending on the stoichiometry, the mononuclear complex [Ir(cod)(HBDP)] or the homodinuclear complex [{Ir(cod)}₂(BDP)]. Both complexes react readily with carbon monoxide to yield the species [Ir(CO)₂(HBDP)] and [{Ir(CO)₂}₂(BDP)], respectively. The results from NMR spectroscopy and X‐ray diffraction reveal different conformations for the tetrapyrrolic ligand in both complexes. The reaction of [{Ir(coe)₂(μ‐Cl)}₂] with H₂BDP proceeds differently and yields the macrocyclic [4e^?,2H⁺]‐oxidized product [IrCl₂(9‐Meic)] (9‐Meic = monoanion of 9‐methyl‐9,10‐isocorrole), which can be addressed as an iridium analog of cobalamin.     

Ferrocenyl-nitrogen donor ligands. Synthesis and characterization of rhodium(I) complexes of ferrocenylpyridine and related ligands

The preparation of a series of complexes of the types [RhCl(CO)₂(L)], [RhCl(cod)(L)] and [Rh(cod)(L)₂]ClO₄, where L is a ligand incorporating a ferrocenyl group and a pyridine ring is described. Complexes were characterized using NMR, IR and electronic spectroscopy. The electrochemical behaviour of the complexes was examined using cyclic voltammetry. The X-ray structures of three of the complexes, [RhCl(CO)₂{NC₅H₄CNC₆H₄(η⁵-C₅H₄)Fe(η⁵-C₅H₅)}], [RhCl(cod)(3-Fcpy)] and [RhCl(cod){3-Fc(C₆H₄)py}], were determined.     

Titanium(IV) and Zirconium(IV) Sulfato Complexes Containing the Kläui Tripodal Ligand: Molecular Models of Sulfated Metal Oxide Surfaces

Treatment of titanyl sulfate in about 60 mM sulfuric acid with NaL_OEt (L_OEt^?=[(η⁵‐C₅H₅)Co{P(O)(OEt)₂}₃]^?) afforded the μ‐sulfato complex [(L_OEtTi)₂(μ‐O)₂(μ‐SO₄)] ( 2 ). In more concentrated sulfuric acid (>1 M ), the same reaction yielded the di‐μ‐sulfato complex [(L_OEtTi)₂(μ‐O)(μ‐SO₄)₂] ( 3 ). Reaction of 2 with HOTf (OTf=triflate, CF₃SO₃) gave the tris(triflato) complex [L_OEtTi(OTf)₃] ( 4 ), whereas treatment of 2 with Ag(OTf) in CH₂Cl₂ afforded the sulfato‐capped trinuclear complex [{(L_OEt)₃Ti₃(μ‐O)₃}(μ₃‐SO₄){Ag(OTf)}][OTf] ( 5 ), in which the Ag(OTf) moiety binds to a μ‐oxo group in the Ti₃(μ‐O)₃ core. Reaction of 2 in H₂O with Ba(NO₃)₂ afforded the tetranuclear complex (L_OEt)₄Ti₄(μ‐O)₆ ( 6 ). Treatment of 2 with [{Rh(cod)Cl}₂] (cod=1,5‐cyclooctadiene), [Re(CO)₅Cl], and [Ru(tBu₂bpy)(PPh₃)₂Cl₂] (tBu₂bpy=4,4′‐di‐tert‐butyl‐2,2′‐dipyridyl) in the presence of Ag(OTf) afforded the heterometallic complexes [(L_OEt)₂Ti₂(O)₂(SO₄){Rh(cod)}₂][OTf]₂ ( 7 ), [(L_OEt)₂Ti(O)₂(SO₄){Re(CO)₃}][OTf] ( 8 ), and [{(L_OEt)₂Ti₂(μ‐O)}(μ₃‐SO₄)(μ‐O)₂{Ru(PPh₃)(tBu₂bpy)}][OTf]₂ ( 9 ), respectively. Complex 9 is paramagnetic with a measured magnetic moment of about 2.4 μ_B. Treatment of zirconyl nitrate with NaL_OEt in 3.5 M sulfuric acid afforded [(L_OEt)₂Zr(NO₃)][L_OEtZr(SO₄)(NO₃)] ( 10 ). Reaction of ZrCl₄ in 1.8 M sulfuric acid with NaL_OEt in the presence Na₂SO₄ gave the μ‐sulfato‐bridged complex [L_OEtZr(SO₄)(H₂O)]₂(μ‐SO₄) ( 11 ). Treatment of 11 with triflic acid afforded [(L_OEt)₂Zr][OTf]₂ ( 12 ), whereas reaction of 11 with Ag(OTf) afforded a mixture of 12 and trinuclear [{L_OEtZr(SO₄)(H₂O)}₃(μ₃‐SO₄)][OTf] ( 13 ). The Zr^IV triflato complex [L_OEtZr(OTf)₃] ( 14 ) was prepared by reaction of L_OEtZrF₃ with Me₃SiOTf. Complexes 4 and 14 can catalyze the Diels–Alder reaction of 1,3‐cyclohexadiene with acrolein in good selectivity. Complexes 2 – 5 , 9 – 11 , and 13 have been characterized by X‐ray crystallography.     

Zinc Hydrazides and Alkoxyhydrazides: Organometallic Compounds with Novel Zn4N8, Zn4N6O and Zn4N4O2 Cage Structures

Tetrameric [{RZn(NHNMe₂)}₄] (R = Me, Et), the first organometallic zinc hydrazides to be described, have been prepared by alkane elimination from dialkylzinc solutions and N,N‐dimethylhydrazine. They were characterised by ¹H and ¹³C NMR and IR spectroscopy, mass spectrometry, elemental analysis and X‐ray crystallography. The compounds form asymmetric aggregates containing the novel Zn₄N₈ core; tetrahedra of Zn atoms bear the alkyl groups at Zn, with the triangular faces bridged by NHNMe₂ substituents. The NH groups are connected to two Zn atoms, and the NMe₂ groups to one. Hydrolysis of the compounds with water gives [(RZn)₄(OH)(NHNMe₂)₃] as products, which also were characterised as described above. Higher yields of these hydroxo clusters were achieved in one‐pot syntheses by reaction of dialkylzinc solutions with mixtures of N,N‐dimethylhydrazine and water. They contain Zn₄N₆O cages, in which one hydroxide in the tetrameric hydrazides described above replaces one NHNMe₂ group. Similar products can be prepared with alkoxy instead of hydroxy groups, in analogous one‐pot syntheses with alcohols. Alcoholysis of [EtZn(NHNMe₂)]₄ with methanol or ethanol gave zinc trishydrazide monoalkoxides, [(EtZn)₄(OR)(NHNMe₂)₃] (R = Me, Et), which have constitutions analogous to the monohydroxides. The organozinc bishydrazide bisalkoxides [(MeZn)₄(NHNMe₂)₂(OEt)₂] and [(EtZn)₄(NHNMe₂)₂(OEt)₂] were obtained in one‐pot reactions from dialkylzinc solutions with mixtures of the hydrazine and alcohol, and their crystal structures, confirmed by spectroscopic methods in solution, show an unsymmetrical aggregation with the novel Zn₄N₄O₂ cage structure.     

An Examination of the Palladium/Mor‐DalPhos Catalyst System in the Context of Selective Ammonia Monoarylation at Room Temperature

An examination of the [{Pd(cinnamyl)Cl}₂]/Mor‐DalPhos (Mor‐DalPhos=di(1‐adamantyl)‐2‐morpholinophenylphosphine) catalyst system in Buchwald–Hartwig aminations employing ammonia was conducted to better understand the catalyst formation process and to guide the development of precatalysts for otherwise challenging room‐temperature ammonia monoarylations. The combination of [{Pd(cinnamyl)Cl}₂] and Mor‐DalPhos afforded [(κ²‐P,N‐Mor‐DalPhos)Pd(η¹‐cinnamyl)Cl] ( 2 ), which, in the presence of a base and chlorobenzene, generated [(κ²‐P,N‐Mor‐DalPhos)Pd(Ph)Cl] ( 1 a ). Halide abstraction from 1 a afforded [(κ³‐P,N,O‐Mor‐DalPhos)Pd(Ph)]OTf ( 5 ), bringing to light a potential stabilizing interaction that is offered by Mor‐DalPhos. An examination of [(κ²‐P,N‐Mor‐DalPhos)Pd(aryl)Cl] ( 1 b – f ) and related precatalysts for the coupling of ammonia and chlorobenzene at room temperature established the suitability of 1 a in such challenging applications. The scope of reactivity for the use of 1 a (5 mol %) encompassed a range of (hetero)aryl (pseudo)halides (X=Cl, Br, I, OTs) with diverse substituents (alkyl, aryl, ether, thioether, ketone, amine, fluoro, trifluoromethyl, and nitrile), including chemoselective arylations.